The isolated perfused rabbit kidney was used to characterize the hormone-sensitive lipid pool from which esterified arachidonic acid is hydrolyzed by the vasoactive hormone bradykinin. The kidney lipids were labeled with radioactive arachidonic acid and the specific activities (counts per min/ng) of the prostaglandin E2 released with or without hormone stimulation were compared. The results indicated the following. The specific activity of prostaglandin E2 released under basal (no hormone stimulation) conditions was 4 to 5-fold higher than the corresponding value after bradykinin administration. The prostaglandin E2 fractions obtained in the absence or presence of bradykinin thus originate from two functionally different pools of esterified arachidonate, designated the hormone-insensitive and the hormone-sensitive pools, respectively. Infusion of exogenous arachidonate to a kidney which was prelabeled with radioactive acid caused the release of prostaglandin E2 having a specific activity markedly higher than that of basal prostaglandin E2, indicating that exogenous arachidonate is incorporated mainly into the hormone-insensitive pool. During the course of the kidney perfusion experiment, the specific activity of the bradykinin-stimulated prostaglandin E2 is gradually increasing. This trend is accelerated if the kidney is repeatedly stimulated with the hormone. We conclude that the rate of arachidonate incorporation into the hormone-sensitive pool is relatively slow and is controlled by the extent to which the pool has been depleted by prior hormone stimulation. Repeated stimulations cause radioactive arachidonate from the hormone-insensitive pool to be transferred to the hormone-sensitive pool to replace the arachidonate that had been hydrolyzed and converted to prostaglandins. Characterization of the hormone-sensitive pool by specific labeling with radioactive arachidonic acid would thus be best achieved under conditions which induce prior release of nonradioactive acid from this pool.
|Number of pages||5|
|Journal||Journal of Biological Chemistry|
|State||Published - 1981|